Diagnosing what has gone wrong in the past few years and how we've ended up on the brink of another crisis is the easy bit. But how do we get out of the mess? What would a "collective and bold action plan", which is what the G20 is promising, look like? There are no easy answers but here are five suggestions:

1. Inject more capital into the European banking system. The IMF is screaming for it, and rightly so if its €200bn-€300bn estimate of the sovereign debt risk is even remotely correct. Fiddling around with the 16 mid-sized laggards who failed, or marginally passed, the summer stress tests is not enough. Big French banks may offer plausible arguments for why their capital cushions are sufficiently plump to withstand more than a Greek default, but markets have moved on. The sheer size of balance sheets is intimidating investors who don't know where the losses will land. More capital is the best way to create confidence. Likelihood factor: 4/5

2. Get the Greek default done. Piling austerity on austerity in Greece is no solution. The numbers don't work, even with mini-haircuts for bondholders announced in July: growth isn't happening and the road to a competitive economy is too long. The debt write-off has to be larger – probably at least 50%. The "orderly" part of default really means a plan to contain contagion. For investors to be confident that Greece is a one-off, the eurozone has to throw protective arms around Portugal, Ireland, Spain and Italy. That means Germany, in particular, has to decide what guarantees it is prepared to give and what it wants to see in return. Likelihood factor: 3/5

3. More stimulus. The risk of inflation is fading fast as recession grows closer and commodity prices fall. The Fed's "operation twist" looks too little to stimulate demand. Stronger medicine is required. That may mean more quantitative easing. But measures to get loans directly into the hands of small businesses may be better. In the UK cutting national insurance, a tax on jobs, may be required. Likelihood factor: 4/5

4. Less austerity. Investors' greatest fear now is lack of growth. With low-term cost of borrowing for governments so low, the case for more spending on infrastructure is strengthening. It's tricky for any government to do it alone without upsetting its local bond market. This is one area where co-ordinated international action is critical. Likelihood factor: 2/5

5. Free the renminbi. Persuading China to loosen its currency peg to the dollar may sound like mission impossible. But imbalances in global trade lie at the heart of the crisis – a new deal for the global economy has to give rebalancing a greater chance of happening. Even China, let's hope, can now see the need to change direction and encourage more domestic consumption and fewer exports. Likelihood factor: 1/5